An organic electroluminescence device is a light emitting device making use of light emission from radiative deactivation of excitons. The excitons are generated by applying a voltage to the organic light emitting layer interposed between a pair of electrodes, and by thereby recombining electrons and holes injected from a cathode and an anode, respectively, into an organic light emitting layer.
There have heretofore been known organic electroluminescence devices using substrates (shaped substrates) processed into the form of mesas in order to enhance light extraction efficiency from an organic light emitting layer (Optics Letters, 22, 396 (1997)).
In such an organic electroluminescence device, a high refractive index layer having a higher refractive index than an organic light emitting layer is formed on a glass substrate, then the high refractive index layer and the glass substrate are shaped to have mesas, and the organic light emitting layer interposed between a transparent electrode and a metal electrode is formed on the high refractive index layer.
Moreover, a metal mirror is formed on sidewalls of the mesa, a polyimide layer to planarize the mesa is formed on the metal mirror, and a metal line contacting the transparent electrode is formed on the polyimide layer.
When light enters the high refractive index layer from the organic light emitting layer, the light traveling in a lateral direction inside the high refractive index layer is reflected by the metal mirror and is bent to travel toward the glass substrate so that the light can be extracted out of the organic electroluminescence device.
In the organic electroluminescence device, the light travels in the lateral direction inside the high refractive index layer while repeating total reflection by an interface between the high refractive index layer and the glass substrate and specular reflection by the metal electrode. Since the high refractive index layer is thin, the light is inevitably reflected a large number of times per unit length.
As a result, the light traveling in the lateral direction is rapidly attenuated in accordance with the number of reflections. Thus, as a distance between adjacent mesas, i.e., a distance between metal lines increases, the light reaching the metal mirror decreases and an improving effect of light extraction efficiency is impaired. This causes a problem of difficulty in producing an organic electroluminescence device with a larger area.
Moreover, there is another problem that manufacturing the organic electroluminescence device requires a lot of time and cost because manufacturing processes of the organic electroluminescence device are complicated.